In liquid operating media in vehicles, heat generated for example by virtue of an energy transformation is given up to a coolant in a heat exchanger so that the utility of the operating medium is maintained and the operating medium remains available for further energy uptake.
Operating media of this type can be lubricants in motors or transmissions, which are heated due to the movement of the components present, or an oil or the water of a hydrodynamic braking device may be concerned, which converts the kinetic energy of the vehicle with the help of blading into heat which is transferred to the operating medium.
Heat exchangers are often designed as shell structures in which a plurality of similar shells are attached over one another and to one another, for example by brazing, which then form passages which respectively carry a coolant and an operating medium to be cooled past one another.
If in a vehicle there are several operating media to be cooled, then either several heat exchangers can be provided, in one of which in each case an operating medium is cooled by a coolant, or more than one operating medium can be cooled in a common heat exchanger, and in that case the heat exchanger has several zones each of which can come into contact with one coolant for the transfer of heat. Such heat exchangers are also known as multi-flow heat exchangers. For example a coolant circuit, a transmission oil circuit and a retarder oil circuit can be connected to a triple-flow heat exchanger.
The separation of the circuits and the guiding of the respective operating media into their associated passages of the heat exchanger take place by way of a tube, particularly a brazed tube, attached between a connection flange and the passages, along the length of which the distribution of the number of passages between the respective operating media can be varied.
Such a multi-flow heat exchanger is known from DE 197 12 599 A1 in which a plurality of oil feeds are provided, each of which is fed into fixed associated passages in order to come into contact with coolants also fed into the heat exchanger for heat transfer.
When operating media should only be used in certain operating conditions of the vehicle and in a particular operating condition only one operating medium should be cooled whereas another operating medium needs no cooling because the other operating medium in the operating condition concerned is not subjected to heat generation stress, then by means of a switching valve the operating medium circuit can be designed so that only the one operating medium flows through all the passages of the heat exchanger, while in the operating condition the other operating medium is not passed though the heat exchanger. The passages assigned to respective operating media during separate cooling are, in the operating condition, connected together for the operating medium to be cooled.
Such switching valves are structurally complex and when connected into the operating medium circuit give rise to high pressure losses.